The transforming growth factor (TGF) beta superfamily proteins are key regulators of fibrosis in all parenchymal organs [Kisseleva et al., Proc Am Thorac Soc. 5: 338-42 (2008)]. Duchenne Muscular Dystrophy (DMD) is characterized by progressive fibrosis that is accompanied by increased TGFβ signaling [Bernasconi et al., J Clin Invest. 96: 1137-44 (1995); Chen et al., Neurology 65: 826-34 (2005)]. In DMD, fibrosis not only contributes directly to muscle dysfunction but also inhibits regeneration. DMD is characterized by muscle membrane fragility that leads to progressive myofiber loss. With disease progression, DMD muscle is replaced by fibrosis. Although muscle is highly regenerative, regeneration in DMD is not sufficient to offset degeneration leading to muscle weakness. Glucocorticoid steroids are used to slow progression in DMD, but use of steroids is complicated by side effects including osteoporosis and weight gain (Bushby et al., 2010). Experimental therapies for DMD include approaches to increase dystrophin expression, modulate the inflammatory response, promote muscle growth and reduce fibrosis [Bushby et al., Lancet 374: 1849-56 (2009)].
In recent years, biological compounds such as antibodies have shown efficacy for treating chronic diseases. For example, antibodies directed against TNFα (infliximab) or anti-TNF receptor (etanercept) are now in wide use for rheumatoid arthritis and other related disorders. While initially developed for its anti-cancer activity, the anti-VEGF antibody is now used to treat macular degeneration (bevacizumab). Thus, long-term use with biological compounds can be effective and safe. Consistent with therapeutic approaches comprising the administration of a biological compound such as an antibody is the fact that antibodies are readily detected in the matrix of dystrophic muscle, such as the muscle of DMD patients.
A number of approaches, including but not limited to angiotensin inhibition, either through the converting enzyme or the angiotensin receptor, aldosterone inhibition, and inhibition by antibodies directed against TGFβ have been or are being tested to reduce fibrosis in DMD. [Cohn et al., Nat. Med. 13: 204-10 (2007); Rafael-Fortney et al., Circulation. 124: 582-8 (2011); Nelson et al., Am J. Pathol. 178: 2611-21 (2011)]. A major limitation of these approaches is that these drugs are systemically active and often have unwanted effects such as reduced blood pressure. Given the relative hypotension of DMD patients, especially advanced DMD patients, such approaches are limited.